1. Field of the Disclosure
The disclosure relates generally to microelectromechanical systems (MEMS) and, more particularly, to MEMS resonator devices.
2. Brief Description of Related Technology
Many types of MEMS resonators are electrostatically actuated. A resonant element of the MEMS device is spaced from stationary electrodes such that the MEMS device is coupled across one or more air gaps. In some designs, the size of the gap between the resonant element and a stationary electrode is significantly less than 1 micron. Vibration of the resonant element varies the spacing between the resonant element and stationary electrodes. To maximize the coupling, the opposing surfaces of the resonant element and stationary electrodes are often large in comparison with the size of the air gap. For example, the surface area in some designs exceeds 1000 μm2.
The large opposing surfaces and small air gap have complicated the fabrication of MEMS resonators. For instance, releasing the resonant element has required a wet etch or other steps in which capillary forces can undesirably pull the resonant element into a collapsed, inoperative condition often referred to as stiction. Stiction has long been recognized as a source of yield loss in MEMS device fabrication.
A number of design solutions and fabrication techniques have been proposed and implemented to minimize stiction-based yield losses. Nonetheless, MEMS device yields often remain unsatisfactorily low due to collapsed resonant elements.